Ozone photolysis of paracetamol in aqueous solution

Abstract

The degradation of a paracetamol (N-acetil-para-aminofenol) aqueous solution (C ⁰ _P = 5 mmol L⁻¹) is studied in a bench-scale setup by means of simple ozonation (O₃) and ozonation catalyzed with UV light (O₃/UV) in order to quantify the influence of UV light on the degradation process. The results have shown that under the adopted experimental conditions (25°C, applied ozone dose = 9.8 mg L⁻¹ and gas flow rate of 20 L h⁻¹) both oxidative systems are capable of removing the substrate with mineralization degrees up to 51% for ozonation and 53% for O₃/UV. HPICE chromatography allowed the detection of nitrate ions and maleic and oxalic acids as ultimate carboxylic acids. The experimental data have been interpreted through 5 indicators: the conversion of paracetamol (X_P ), the conversion degree of TOC (X_TOC ), the apparent rate constant (k_ap ), the Hatta number (Ha) and the enhancement factor (E). The main advantage of photo-ozonation compared to simple ozonation was a more advanced conversion (79% vs. 92% after 90 min). The paracetamol decay follows a pseudo–first-order reaction with a superior rate constant (higher by 54%) for the UV catalyzed system in comparison with direct ozonation. Mineralization is slightly accelerated (+4%) in the O₃/UV system, due to the additional production of hydroxyl radicals induced by the UV light and a higher Hatta number (+24%). Nevertheless, the process was still in the slow reaction kinetic regime (Ha < 0.3), and the enhancement factor was not significantly increased. The results are useful for the design and scale-up of the gas-liquid processes.

Keywords:

• Ozonation
• paracetamol
• advanced oxidation process
• ozone photolysis
• rate constant
• enhancement factor

Acknowledgments

Experiments were performed at the Helmholtz Zentrum-München, German Research Center for Environmental Health, Institute of Ecological Chemistry (formerly GSF-National Research Center for Environment and Health), and at the Technical University in Munich, Germany. Maria Bobu wishes to express her gratitude to the Erasmus Program.